Scholar Rock wins first FDA approval for Isembyld in spinal muscular atrophy

Scholar Rock has received its first regulatory approval, with the U.S. Food and Drug Administration clearing its injectable therapy Isembyld for a rare genetic condition that causes progressive muscle weakness.

The drug is the first muscle-targeted treatment designed to improve motor function in adults and children with spinal muscular atrophy who have already been treated with existing therapies for the disorder. The company said Isembyld would be available in the coming days, but did not immediately respond to a request for comment on pricing.

News of the approval lifted Scholar Rock's shares by more than 23% in after-market trading.

Spinal muscular atrophy damages motor neurons, leading to worsening muscle weakness and difficulties with movement, breathing and swallowing. The Muscular Dystrophy Association estimates that roughly 10,000 children and adults in the United States live with the condition.

Isembyld, chemically known as apitegromab, works by selectively blocking activation of myostatin, a protein that restricts muscle growth, with the goal of building muscle mass and strength. The approval rests on late-stage data showing the therapy significantly improved motor function compared with placebo.

The spinal muscular atrophy treatment landscape includes Biogen's Spinraza, Novartis' gene therapy Zolgensma and Roche's oral Evrysdi. Scholar Rock has previously said it would manufacture Isembyld at a U.S.-based facility.

Cantor analysts described the approval as positioning Scholar Rock as one of biotech's strongest long-term growth stories, citing potential geographic, indication and product-line expansions. BMO Capital Markets analyst Evan Seigerman forecasts adjusted worldwide peak sales of $2.1 billion by 2035.

The company is also testing the drug to preserve muscle in obesity, a field where more than a dozen companies are developing treatments aimed at limiting muscle loss during weight loss.